Suggested fix for morris#97, review of implications required

With the prepended slash, minimatch will never actually return an object with negate: true, so it's impossible to ignore files in clean operations. Please review this change and consider implications to the remaining codebase - perhaps even consider refactoring to use the glob processing implementation in vinyl-fs, that also gulp.src uses, if possible?

lib/glob.js

@@ -14,7 +14,7 @@ function glob( globs, options ) {
 	var negatives = [];
 	globs.forEach( function ( glob ) {
 
-		var mm = new Minimatch( self.join( '/', glob ), options );
+		var mm = new Minimatch( glob, options );
 		mm.base = mmBase( mm );
 
 		if ( mm.negate ) negatives.push( mm );